Ignitron system



g- J. SLEPIAN IGNITRON SYSTEM Filed Sept. 21, 1938 3 Sheets-Sheet l INVENTOR Joseph J/ep/m. BY

' WI FNESSES:

ATTORNE J. SLEPIAN Aug. 6, 1940.

IGNITRON SYSTEM Filed Sept. 21, 1958 3 Sheets-Sheet 2 INVENTOR Joseph filep/km. BY

WITNESSES:

ATTORNEY azw. 4 %w S I M Joseph J/ep/an. M v BY (%w- J. SLEPKAN 2,210,690

' IGNITRON sYs'rxas Filed Sept. 21, 1939 s Sheets-Sheet s WITNESSES: INVENTOR Patented Aug 6, 1940 UNITED, STATES PATENT OFFICE IGNITRON SYSTEM Joseph Slepian, Pittsburgh, Pa., assignor to 'Westinghouse Electric & Manuiacturing Company, East Plttsburglnla... a corporation oi Pennsylvania Application September 21, 1938, Serial No. 230,979

11 Claims. (01. 175-354) My invention relates to circuits in which a plurality of electrical discharge devices are connected respectively in the difierent phases of an alternating-current system to conduct current to or from a direct-current system, and, in particular, relates to circuits of the foregoing type in Still another object of my invention is to providean arrangement whereby fluctuations oi the direct-current output voltage during each alterhating-current cycle of a system in which-a plurality of electrical discharge devices are connected to the respective phases of an alternatingcurrent source shall be minimized.

A Iurther object of my invention is to provide an arrangement whereby dissimilarities in conductivity between a plurality of gaseous electrical discharge devices connected to transmit current from the respective phases oi an alternating-current system to or from a direct-current system may be prevented from causing dissymmetrical fluctuations oi the direct current during the alternating-current cycles; r

A still further object of my invention is to provide an arrangement whereby dissimilarities in the conductivity of a'plurality of electrical discharge devices respectively connected to the various phases of an alternating-current line to conduct current to or from a direct-current line shall be prevented from causing uneven distribution of load current between the different electrical discharge devices.

Other objects of my invention will become apparent from reading the following description, takenin connection with the drawings in which:

Figure 1 illustrates a pair of electrical discharge devices connected to line-terminals of a single-phase alternating-current circuit and provided with arrangements embodying the principles of my invention;

Fig. '2 shows a similar arrangement of two discharge devices connected to a single-phase to provide ahave any predetermined ratio to each other.

, line and provided with a different arrangement embodying the principles of my-invention;

Fig. 3 shows anarrangement of six electrical discharge devices connected to a six-phase alternating-current system'and provided with arrangements embodying the same principles as Fig. 2 .of my invention;

Fig. 4 illustrates a circuit connection in which three electrical discharge devices connected to the respective phases of a three-phase line are.

provided with arrangements embodying still another modiilcation of my invention; and

Fig. 5 shows an arrangementin which six electrical discharge devices are connected to the respective phase terminals of a six-phase alternating-current line and are provided with circuits embodying still another modification of my invention.

Electrical systems in which 'a plurality of electrlcal discharge devices are respectively connected to the diilferent phase terminals of alternating-current circuits are well known, and where the discharge tubes are substantially identical in their electrical properties, i. e. particularly in their electrical conductivity, they will divide the load current equally between them in the conventional case where the circuits constitute a symmetrical system. Dividing the load current equally between them? means, in the present instance, at the average value through the a]:- ternat -current cycle of the currents in diiierent tubes is the same, although, oi-course. the instantaneous values at any one particular moment differ from each other. However, in practical rather than ideal cases, the electrical characteristics of the discharge tubes are likely todifler somewhat, and even if the other components of the electrical circuits are ideally symmetrical, the various electrical discharge tubes will then not divide the current equallyr Furthermore, even slight dissymmetries in the electrical elements constituting the different phases of the alternating-current system will cause unequal division of load even were the electrical discharge tubes ideally identical with each other.

To take one instance of the foregoing, electrical discharge devices of the type known as Ignitrons are likely to exhibit dissimilarities. An Ignitron tube consists of an anode,'a cathode usually of mercury and a so-called igniter electrode, the latter comprising a rod of some high resistance material, such as boron carbide, which dips into the mercury and which is caused to initiate ionization adjacent the cathode surface early in those half cycles'of the alternating supply voltage which makes the line terminal to which the anode is connected positive. The ionizing effect is produced by a sudden flow of current through the igniter electrode, and the instant in the alternating-current cycle at which ionization is initiated can be predetermined by properly timing the initiation of current through the igniter electrode. For ,further description of Ignitron tubes, reference is made to Slepian and Ludwig Patent No. 2,069,283, granted February 2, 1937. In the case of such Ignitron tubes, slight unavoidable dissimilarities in the igniter electrodes and tube conditions may cause slight variations in the precise instant in the alternating-current cycle at which current flow between the anode and the cathode rises to full value.

It can be shown that where two electrical, absolutely identical, discharge tubes are connected in a symmetrical systemof the type shown in Fig. 1, the voltage and current in one tube will be identical with the voltage and current in the other tube, except that they will be displaced in time from each other by 180 electrical degrees of the voltage wave in the supply system. Such being the case, the wave form of the potential difference between the two anodes will show no even harmonics of the alternating-current line frequency. On the other hand, if the two tubes are not absolutely identical, or if there is a dissymmetry in the alternating-current circuits so that one tube carries more current than the other, it can be shown that even harmonics will exist in the potential difference measured between the tube anodes. Where the supply approximates closely to a sine wave, it will usually be found that the second harmonic will be pronounced in the potential difference between the two anodes.

It is the conventional practice to supply current to the respective igniter electrodes of the different tubes through a grid-controlled electrical discharge device. I have discovered that by deriving a second harmonic voltage from a circuit connected across the two anodes of the two-tube system shown in Fig. 1 and impressing it :in proper magnitude on the control electrode of the tube supplying current to the igniter electrode,

I can neutralize the tendency of either of the two principal discharge tubes to conduct more than its share of the load current, I have also found it possible to derive second harmonic voltages from other portions of a system involving two tubes and to use these voltages to compensate any tendency toward unequal division of current between the tubes. I have also discovered that it is possible to derive harmonic voltages other than the second which may be applied in the case of three-phase systems, six-phase systems or the like to similarly compensate tendencies toward unequal division of load between the tubes in such systems. I have, in fact, discovered general methods by which a discharge tube system of any number of phases, such as n phases, may be made to supply voltages of the proper harmonic frequency to compensate any tendency toward unequal division load current between the tubes used in the n-phase system.

Referring to Fig. 1 of the drawings, with the foregoing principles in mind, an alternating-current source I, which may be the secondary of a transformer supplied with sinusoidal singlephase voltage, has its respective terminals connected to the anodes of two electrical discharge tubes 2 and 3 which I have shown as being of the Ignitron type. The cathodes of these electrical discharge tubes are both connected to the positive terminal of a direct-current load circuit, the negative terminal of this circuit being connected through an inductance 5 to the midpoint of the secondary I. Each of the Ignitron tubes is provided with an igniter electrode 6 which dips into a mercury cathode 'l. The igniter electrode of tube 2 is supplied with current through a gridcontrolled electrical discharge tube 8, and a similar discharge tube 9 supplies current to the igniter electrode of tube 3. The tube 8 includes, besides an anode If and an excited cathode I2, a control electrode I3 which is connected to the v circuit of its anode and cathode by the secondary M of a transformer, A bias battery l4 may be provided to impress a bias-voltage on control electrode l3, This transformer has a primary l5 which is connected through a capacitor l6 and a resistor H in shunt between the anodes of the tubes 2 and 3. A similar secondary l8 controls the potential of the control electrode IQ of tube 9. The polarity of windings l4 and l5 i made such that, when the end of winding 15, which is nearest to tube 2, is positive, the end of winding I4, which is connected to grid I3, is more positive than its other end. Conversely when that end of winding M which is connected to its grid I3 is positive. the polarity of winding l 8 is such that that end of it which is connected to grid i9 is more positive than itsother end.

The capacitor l6 and the winding l5 are tuned to the second harmonic of the sinusoidal voltage supplied to winding I, and the value of resistor I! is adjusted to maintain the current flowing through the shunt circuit embodying it within a reasonable value. The value in ohms of resistor ll should in general be small compared with that of condenser I6 at the frequency to which l5 and i6 resonate. The voltage impressed by the winding I 4 upon the control electrode l3 may thenbe adjusted to such a value that an ammeter, connected directly in series with the anode of tube 2, shows substantially the same value as does a similar ammeter connected directly in series with the anode of tube 3.

To illustrate a typical circuit embodying my invention, the secondary winding I may impress a sinusoidal voltage of 1200 volts at 60 cycles upon the tubes 2 and 3. The latter may be Ignitron tubes of the type WL656, manufactured by Westinghouse Electric & Manufacturing Company, rated at 600 volts and 100 amperes. The igniter electrodes 6 are rated at 15 amperes, and the tubes 8 and 9 may be tubes of the type 628, manufactured by Westinghouse Electric & Manufacturing Company, and rated at 10 amperes and 1000 volts. The capacitor It may be of 10 microfarads: the winding l5 have an open-circuit inductance of about 100 millihenries; and the resistor ll be of 0 ohms. The windings I l and 18 may each derive a voltage which is 100 percent of that across the terminals of the winding i5.

Referring now to Fig. 2 of the drawings, a sinusoidal alternating voltage may be supplied by a winding I having Ignitron tubes 2 and 3 connected to its terminals in a way which requires no separate description because it is identical with Fig. 1. It can be shown that where two tubes, such as are here shown, are ideally identical with each other and the connections of the winding 8 and its load circuit are ideally symmetrical, the voltage between the midtap of winding I and the cathodes of tubes 2 and 3 contains only even harmonics of the aforesaid sinu- 85 the same voltage from the same three-phase prisoidal voltage. on the other hand, if one of the tubes 2 and 3 differs in electrical characteristics from the other so that the current is divided unequally between them, voltages which are odd harmonics of the aforesaid sinusoidal voltage will appear between the cathode 1 and the aforesaid midtap.

In most cases, it will be found that the iirst harmonic of the aforesaid sinusoidal voltage (1. e.

the fundamental frequencyitself) will be the most pronounced of these odd harmonics. 1, ac-

cordingly, connect a primary winding 2| in series with a capacitor 22 and a resistor 23 between the cathode 1 and the aforesaid inidtap. I then connect a secondary winding 24, influenced by the primary 2|, betweenthe grid electrode |3 of its cathode and anode.

the tube 8 and some point on the circuit between For example, the winding 2 4 may be connected through a bias-battery 24' between the anode and the grid l3, as illustrated. I connect a similar secondary winding 25 between the grid and anode circuit of the tube 9.. I make the polarity of the windings 24 1 and 2| such that the end of winding 24, which is connected to grid l3, is positive when the end of winding 2| adjacent the aforesaid mid-tap connection is positive relative to its other end. I

then adjust the capacitor 22 and the winding 2| so that they are tuned to the fundamental frequency of the above-mentioned sinusoidal wave, and adjust the value of resistor 23 so that the current flowing through capacitor 22 is of a safe value. This adjusted value will in generalbe small relative to the 'reactance of condenser 22 at the frequency to which condenser 22 and inductance 2| resonate.

variable tap connection thereon and an ammeter rating of a similar ammeter connected in series 1 connected directly in series with the anode of tube 2 shows the nearest possible equality to the Y with the anode of tube 3.

, per terminal when the lower terminal of winding 24 is positive relative to its upper terminal.

In Fig. 3, I have shown how the principles used in connection with Fig. 2 may be applied to a sixphase rectifier of the type sometimes referred to as diametrical three-phase. In this arrangement, a Y-connected three-phase transformer secondary comprising three windings 3|, 32, 33 may be supplied with power from a three-phase primary winding, not shown, and may have its three-phase terminals respectively connected to three Ignitron tubes 34, 35, 36, as shown in the drawings. A similar set of three-phase secondaries 31, 38, 39 may be supplied with current of mary, and the free terminals of windings 31, 38 and 38 may be connected respectively to the anodes of three Ignitron tubes 4|, 42 and 43. As is indicated in the drawings, the voltage impressed by winding 31 on the anode of tube 4| is 180 degrees out of phase with the voltage impressed on the anode of tube 34 by the winding 3|, and a similar relationship exists between the voltages of the other secondary windings-men- The voltage of secondary winding 24 may then be adjusted by moving a rent rating of 100 amperes.

tioned. The cathodes I of the Ignitron tubes above-mentioned are connected to the positive terminal of adirect-current load,-the negative terminal of thelatter being connected through an inductance 44 'to the midpoint 45 of an equalizer winding 46 of a type too well known in. the rectifier art to require detailed description. "I'he end terminals of the winding 46 are respectively connected tothe center terminal of the viously described.

-'two sets of Y-connected secondary windings pre- .The igniter'electrodes 6 of the above-men- I tioned Ignitron tubes 34, 35, 36, 4|, 42, 43 are respectively supplied with currentthrough gridcontrolled discharge tubes 41, 48,349, 5|, 52, 53 similar to tubes 8 and 9 of Fig. 1. 1

1 have'found that, when the windings 3|,"32, as, 4

31, 38, 38 generatea set of six absolutely symmetrical six-phase voltages and the tubes 34, 35, 36, 4|, 42, 43 are identical in their electrical "characteristics, and the electrical system is" otherwise perfectly symmetrical, the voltage appearing between the tap 45and the common cathode terminals of the Ignitron tubes contains no third harmonic of the fundamental frequency of the above-mentioned sinusoidal voltage. 0n I the other hand, where the mean value during the alternating-current cycle of the current supplied by the group of windings 3|, :2, 3a differs from the mean value of the current supplied by the group of windings 31, 38, 39, athird harmonic of the aforesaid sinusoidal voltage-appears between the tap 45 and the common cathode terminals of the Ignitron tubes.

p In order to neutralize such a tendency of the two aforesaid groups to divide current unequally,

, I connect between the tap point 45 and the cathodes of the Ignitron tubes a primary winding 54 in" series with a variable capacitor 55 and a variable resistor 56. The capacitor 55 and the opencircuit inductance of primary 54 are tuned to the thirdharmonic of said sinusoidal voltage, and the fvalue of resistor 56 is adjusted until the current through it is of a safe value, the resistor having an adjusted resistance which is small compared to the reactance at the third harmonic frequency of capacitor 55. 'I then connect a secondary winding 51 between the grid of tube 41 andsome point on its. anode-t -cathode circuit, such as its anode. I connect similar secondary windings 58, 59, 60, 6|, 62, respectively, to the grid electrodes of tubes 48, 48, 5|, 52, 53. I make the relative polarities of the windings 54 and 41 such that the end of winding 41, which connects to grid I3, is

positive relative to its other end when the end of winding 54, which is nearer to the tap point 45, is positive relative to its other end. I make the polarities of windings 58, 58, 68, 6| and 62 the same relative to winding 54, as I have just described for winding 51, relative to its other terminal. 7

To describe a typical embodiment of my invention, the tubes 34, 35, 36, 4|, 42, 43 may be identical with the tube 2 described abo e in connection with Fig. l, and the tubes 41, 48 48.'5|.

- 52, 53 may beidentical with the tube 8 described in connection with Fig. 1. The transformer windings 3|, 32, 33. 31, 38, 39 may each have'a voltage of 600 volts at cycles and have a cur- The equalizing winding 46 may have an open-circuit inductance of- 10 henries and have a current rating of 600 amperes. The primary winding 54 may have an open-circuit inductance of about IOU-millihenries;

the capacitor 55 may be of 1 microfarad. The

I I8 and the resistor II shown in Fig. 1.

winding 41 may have a suflicient number of turns so that it has a terminal voltage which is 100 percent of the terminal voltage across winding 54. The windings 58, 59, 68, 5|, 62 may then be of the same number of turns as winding 41.

Referring to Fig. 4 of the drawings, six identical secondary windings II, I2, [9, I4, I5, I5 may be supplied with sinusoidal voltagefrom a pri-' mary winding, not shown. The windings II, I2, I3, 14, 15, I8 being as shown connected in star .to form a symmetrical six-phase system, their respective free terminals may be connected to the anodes of six Ignitron tubes, ofwhich it will be suflicient to show three, 11, I8, I9, the others being connected in exactly the same way to windings I4, 15, I5. Each one of these may be of the same type as the tube 2 in Fig. 1. The three Ignitron tubes II, I8, 19 are respectively. supplied with igniter current by three grid-controlled discharge tubes 88,. 8|, 8!, each of'which may be identical with the tube 8 in Fig. 1. The remaining three Ignitron tubes are provided with three similar igniter tubes. The cathodes l of the Ignitron. tubes may be I'connected to one terminal of a direct-current circuit, the other terminal thereof being connected through an inductance .83 to the neutral point 84 of the star-connected windings II, I2, 13, I4, 15, I8.

Between the anode of each Ignitron tube and the anode of each tube adjacent to it is connected a current channel comprising a primary winding, a variable capacitor and a variable resistor similar, respectively, to the winding 15, the capacitor In order to simplify the drawings, only those channels which connect the anode lead of one Ignitron tube numeral 98.

18 to the anode leads of its adjacent tubes II and 19 have been shown in Fig. 4, but it is to be understood that an exactly similar channel interconnects Ignitron II with the adjacent Ignitron (not-shown) the anode of which connects with the free terminal of winding 88; that a sim- .ing in the channel connecting the anode of the tube I8 with that of tube I9 has the reference numeral 88, the capacitor has the reference numeral 89 and the variable resistor the reference The' capacitor for the channel interconnecting Ignitron II with thelgnitron adjacent it. on the left has the reference numeral 9i, and the resistor of the channelconnecting Ignitron I9 with j the adjacent Ignitron on its right bears the reference numeral 92. In operating the above-described system, the inductance and the capacitor 86 are tuned to a sixth harmonic of the sinusoidal supply voltage mentioned above. Resistor 81 is then adjusted so that the current through winding 85 is kept down to a safe value, its value in ohms being small com-.--

pared to the reactance at the sixth harmonic frequency of capacitor 85. Similar adjustments are made for the primary windin capacitor and resistor in each of the other above-mentioned current channels.

Primary winding as is provided with a pair of secondary windings 94, 95. Primary winding 8 winding 85 is positive; and vice versa. The same relationship exists between the secondary windings 96, 91 and their primarywinding 88; and so on for all the secondary windings which are associated with the other pairs of Ignitrons i'orm ing the complete system. The polarities of the secondary windings being as indicated above, the

right-hand end of winding 94 is connected to the anode of tube 18, and a variable tap on winding'94 is then connected to a variable tap on the left-hand end of winding 91. The righthand end of winding 91 is then connected to the grid of the three-electrode tube 8|, which supplies the igniter current to Ignitron 18. In an exactly similar way, the grid of three-electrode tube 88, which supplies the igniter current to Ignitron II, is connected to the right-hand end of the secondary winding 95, and the variable tap.

on the winding 95 is connected to a lead 98 which extends to a variable tap near the left-hand end of the secondary winding which occupies the same relative position in the current-channel between Ignitron II and the Ignitron on its left that winding 94 occupies in the current channel lconnecting Ignitron I8'with Ignitron 'I'I.

Ina similarway, the right-hand end of secondary winding 96 is connected to the anode of Ignitron I9, and a variable tap near its left end is connected through a lead 99 to the secondary,

winding which occupies the same relative position in the current-channel connecting Ignitron 19 with the adjacent Ignitron at its right that secondary 91 occupies in the current-channel connecting Ignitron 18 with Ignitron I9.

,A moments consideration will show that the repetition for all the six Ignitrons of the connections "just described for the secondary windings 94 and 9'! inconnection with Ignitron I8 will produce an absolutely symmetrical set of connections interlinking all of the Ignitrons, and that while these connections are shown for the three adjacent Ignitrons 11, I8, 19, the circuit diagram represents the complete interconnections of any three adjacent Ignitrons in the complete system.

To describe one specific embodiment of the system shown in Fig. 4, the Ignitron tubes may each be of the same type as the tube 2 described in connection with Fig. 1, and the grid-controlled discharge tubes 88, 8|, etc. may be of the same kind as tube 8 described in connection with Fig. 1.

The transformer windings II, 12, I3, 14, 15, I8.

may each have a ratingof 600 volts and 100 amperes at 60 cycles and form a symmetrical star-connected six-phase system. The primary 85 may have an open-circuit inductance of about 100 millihenries. The condenser 86 may have a capacity of 10 microfarads. The two secondary windings 94 and 95 may each produce a voltage which is '100 percent of the terminal voltage of t primary 85.

In Fig. 5,,1 disclose another modification of my invention which is-adapted to equally divide current between six Ignitrons connected ina balanced six-phase system of the type frequently referred to as a diametrical three-phase. This system comprises one set of three Y-connected secondary windings IOI, I02, I03 in which are induced a symmetrical set of three-phase sinusoidal voltages derived from a primary winding, not shown. The free terminals of the windings IOI, I02, I03 are, respectively, connected to the anodes of three Ignitrons I04, I05, I00, each of the same type as the tube 2 in Fig. 1. The igniter electrode current for the three Ignitrons I04, I05, I06 are, respectively, furnished by three grid-controlled auxiliary tubes I01, I08, I09, which may be similar to the tube 8 described in connection withFig. 1. A second set of Y-connected three-phase windings III, H2, H3 derives current from the above-mentioned set of primary windings (not shown) and has its free ends connected to the anodes of a second set of three Ignitrons I It, I I5, II6 as nearly as possible similar to the Ignitrons I04, I05, I06.

As is indicated by Fig. 5, the voltage in the winding III is equal to but opposite in phase to the voltage in winding IOI so that the voltages in the six enumerated windings constitute a-set of symmetrical six-phase voltages. The tubes H4, H5, H3 are, respectively, supplied with igniter current by a set of grid-controlled tubes H1, H0, III! of similar type to the above-described tubes I01, I08,.III9. The cathodes of all the six Ignitron tubes are connected to one terminal of a direct-current load system, the negative terminal of which is connected through an inductance I2I to the midtap I22 of an equalizer winding I23 of well known type. The free terminals of the winding I23 are, respectively, connected to the central points of the two sets of three-phase windings already described.

- I have found that, when such a six-phase system of Ignitrons and windings, as I have just described, has absolutely identical circuit elements in each of its phases, the voltage between the cathode terminal I20 and the tap I22 contains no harmonics except the sixth harmonic of the above-mentioned sinusoidal voltage. On the other hand, when some dissymmetry exists between the various phases, other harmonics appear between the terminals I20 and I 22. In most cases, I have found that the principal harmonics which thus appear are the first, the second, the third, the fourth and the fifth. I find that by deriving from a channel interconnecting the terminals I20 and I22 a set of harmonic voltages which exclude the sixth and its integral multiples and impressing these voltages on the control'electrodes'of the tubes I01, I08, I09, H1, H8, II3, I can minimize the tendency of the abovementioned other harmonic groups characterizing unequal load division to flow in the circuit, thereby approximating a condition of equal division of load between the Ignitrons.

Corresponding with the foregoing principle, I interconnect the terminals I20 and I22 by a channel comprising; a primary winding I24, a variable capacitor I25 and a variable resistor I23. Across the terminals of the primary winding I24 I shunt one circuit tuned to the sixth harmonic and comprising an inductance I21 and a variable capacitor I23; a second circuit tuned to the twelfth harmonic comprising an induct'-' ance I29 and a variable capacitor I30. In order to obtain still greater refinement, I may similarly shunt the winding I24 with a circuit comprising an inductance and capacitor tuned to any other multiple of the sixth harmonic.

Between the grid of the tube I and some point on its anode-cathode circuit, which may if desired be at the anode, I connect 'a secondary winding I3I which is in inductive relation to the primary I2 3. I make the relative polarities of the windings I24 and I3I such that, when the lower end of the winding I is positive, the lower end of the winding I3I is positive. Windings I32, I33, I30, I35, I36, exactly. similar to .winding I3I, are also provided as secondary In order to operate the system of Fig. 5, the

open-circuit inductance of the winding I2d and the capacitor I25 are tuned ,to the frequency of the sinusoidal supply voltage mentioned above. The resistor I26 is adjusted to such-a value as to hold the current through capacitor I25 to a safe value, but its resistance should be small relative to the reactance at the frequency of the supply voltage of capacitor I25. The inductance I21 and the capacitor I28 are then adjusted so that they resonate at the frequency of the sixth harmonic of the aforesaid sinusoidal voltage. The inductance I29 and the capacitor I30 are then tuned to resonate at the twelfth harmonic of the above-mentioned sinusoidal voltage.

I have described the principles of my invention as applied to a Single-phase system and also as applied to a six-phase system. In order to show how the system may be applied to a system of any desired number of, say, 11., symmetrical phases, I would note that where the primary winding of the compensating transformer is located in a channel interconnecting the anodes of two adjacent rectifiers of an n-phase system, each such channel is tuned to the nth harmonic of the sinusoidal supply voltage. This is true, for example, of Fig. l where the supply transformer has two phase-terminals each connected to the anode of a rectifier; and is similarly true of Fig. 4 where the supply transformer has six phase-terminals each connected to the anode of a rectifier. In the case .of Fig. 1, the channel containing transformer primary I5 is tuned to the second harmonic of the supply voltage, and in the case of Fig. 4, the transformers, primaries 05, 88, etc.

are each contained in a channeltuned to the v sixth harmonic of the supply voltage.

On the other hand, where the primary of the compensating transformer is connected between the terminals of the direct-current load circuit, the channel containing it is-tuned to some harmonic other than the nth. This other harmonic preferably is the one shown by measurements or by experience to be most prominent when the currents divide unequally between the rectifier tubes. Usually this will be found to be the (n+1)th harmonic or the (n+1)th harmonic.

It will be recognized that no completely general It is, accordingly, frequently advisable to tune the compensating channel bridging the direct-current load to first one harmonic after another and to select that arrangement which causes the most even distribution of current between the various rectifier tubes. In the'case of the arrangement of Fig. 5, it will be evident that the shunt circuits which bridge the compensating transformer should be tuned to resonate at the nth, the two nth, the three nth, etc. harmonics of the fundamentals.

While I have described my arrangement as applied to Ignitrons, it will be recognized that the system is not confined to this particular type of tube, but may be applied where the Ignitrons are replaced by any type of discharge tube employing control electrodes. The system is, for example, applicable, not only in the case of gaseous discharge tubes, but even in the case of high-vacuum tubes. I will also point out that where the main power tubes are of types which do not require such auxiliary tubes as the grid-controlled tubes 8 and 9 in Fig. 1, the leads shown as connected to the control grids l3 in the present drawings may be connected to control electrodes in the main discharge tubes themselves.

In accordance with the patent statutes, I have described several specific embodiments of my invention, but the principles thereof are of broader application, as will be evident to those skilled in the art. I accordingly desire that the following claims shall be given the broadest interpretation of which their terms are susceptible in view of the prior art.

I claim as my invention:

1. An electrical translating system comprising a six-phase alternating-current network having connected to each phase terminal an electrical discharge device having a control circuit, an electrical channel tuned to the sixth harmonic of the frequency of said alternating-current network bridging two phase-terminals thereof, and means energized by said channel to impress a voltage of said sixth harmonic frequency on said control circuit.

2. An electrical translating system comprising a six-phase alternating-current network having connected to each phase terminal an electrical discharge device having a control circuit in which current flow initiates conduction by said device,

' an electrical channel tuned to the sixth harmonic of the frequency of said alternating-current network bridging two phase-terminals thereof, and means energized by said channel to impress a voltage of said sixth harmonic frequency on said control circuit.

3. An electrical translating system comprising a six-phase alternating-current network having connected to each phase terminal a gaseous electrical discharge device having an igniter contacting the surface of its cathode and having a control circuit supplying current to said igniter,

an electrical channel tuned to the sixth harmonic of the frequency of said alternating-current network bridging two phase-terminals thereof, and means energized by said channel to impress a voltage of said sixth harmonic frequency on said control circuit.

4. An electrical translating system comprising a six-phase alternating-current network having connected to each phase terminal a gaseous electrical discharge device having an igniter contacting the surface of its cathode and having a control circuit supplying current to said igniter and embodying an electrical discharge tube provided with another control circuit, an electrical channel tuned to the sixth harmonic of the frequency of said alternating current network bridging two phase-terminals thereof, and means energized by said channel to impress a voltage of said sixth harmonic frequency in said control circuits.

5. An electrical translating system comprising an alternating-current network having connected to each phase-terminal an electrical discharge device having a control circuit, means to impress a second harmonic .of the alternating-current voltage to control current flow in said control circuit, and a circuit having a frequency different from that of said network connected to exchange power therewith through said electrical discharge devices.

6. An electrical translating system comprising an n-phase alternating-current network having connected to each phase-terminal an electrical discharge device having a control circuit, means an n-phase alternating-current network having connected to each phase-terminal an electrical discharge device having a control circuit, a current channel tuned to the nth harmonic of the frequency of said network bridging a phase of said network, and means to impress a voltage derived from said channel to control current flow in said control circuit.

8. An electrical translating system comprising an n-phase alternating-current network having connected to each phase-terminal a gaseous electrical discharge device having an igniter contacting its cathode, a control circuit supplying current to said igniter, and means to impress a voltage which is an nth harmonic of the frequency of said network upon said control circuit.

9. An electrical translating system comprising an n-phase alternating-current network having connected to each phase-terminal a gaseous electrical discharge device having an igniter contacting its cathode, a control circuit supplying current to said igniter, a current channel tuned to the nth harmonic of the frequency of said network connected across one phase thereof, and means to impress a voltage derived from said netwoit'sk to control current flow in said control circui 10. An electrical translating system comprising an n-phase alternating-current network having connected to each phase-terminal a gaseous electrical discharge device having an igniter contacting its cathode, a control circuit supplying current to said igniter and embodying a tube having a control circuit, and means to impress a voltage which is an nth harmonic of the frequency of. said network upon the last mentioned 

